Natural radioactivity in some major rivers of coastal Karnataka on the southwest coast of India

Systematic studies on radiation level and distribution of radionuclides have been carried out in riverine environs of three major rivers of coastal Karnataka, viz. Kali, Sharavathi and Netravathi. The ambient gamma radiation levels along three rivers were measured using a portable plastic scintillometer. Activity concentrations of 226Ra, 232Th and 40K in soil, sediment and rock were measured using a NaI(Tl) gamma-ray spectrometer. In the Kali, Sharavathi and Netravathi riverbanks, the median values of absorbed gamma dose rates in air were found to be 44 nGy h−1, 35 nGy h−1 and 57 nGy h−1, respectively. The highest activity of 226Ra was found in riverbank soil samples of Sharavathi River. The highest activities of 232Th and 40K were found in riverbank soil and sediment samples of Netravathi River. In Kali River, the highest 226Ra activity was recorded for rock samples. To assess the radiological hazard of natural radioactivity in the samples, absorbed gamma dose rates in air, radium equivalent activity, representative level index, external hazard index and internal hazard index associated with the radionuclides were calculated and compared with internationally recommended values. The representative level index (Iγr) values are high in sediment samples of Netravathi River. The radium equivalent activity (Raeq), external hazard index (Hex) and internal hazard index (Hin) values are high in rock samples of Kali River. The results of these investigations are presented and discussed in this paper.